(a) Field of the Invention
The present description relates to an apparatus for transmitting and receiving data through an unlicensed band.
(b) Description of the Related Art
As the number of mobile Internet users through a mobile communication system is increased, mobile communication operators is seeking an efficient method for increasing capacity of the mobile communication system. The most efficient and intuitive method is to increase a bandwidth by additionally securing a licensed band frequency for the mobile communication system. However, the licensed band frequency has an advantage that an efficient mobile communication service may be provided through monopolistic use of a corresponding frequency, but has disadvantages that permission and use costs of a frequency are high and a licensed band frequency allocated for the mobile communication system is limited. Therefore, mobile communication operators and manufacturers are studying a method for providing a mobile communication service using an unlicensed band frequency in which available frequency bands are relatively many and a cost is cheap, a TV White Space, or a frequency (hereinafter, referred to as an ‘unlicensed band frequency’) of licensed/unlicensed bands, or the like, shared between mobile communication system operators.
A communication system installed at the unlicensed band frequency has the following limitations.
First, transmission power is limited in order to minimize an influence on another system sharing the unlicensed band frequency. Therefore, in the case in which a licensed band system and an unlicensed band system are installed at the same position, a coverage hole may be generated.
In addition, the unlicensed band frequency should be discontinuously or randomly used for the purpose of fair coexistence with an adjacent unlicensed band system. Therefore, transmission reliability of a control channel and a common channel of the mobile communication system may be decreased.
In addition, a communication system should follow a frequency regulation of the unlicensed band. A system using the unlicensed band frequency should be operated on the basis of a listen before talk (LBT) for the purpose of transmission of data. For example, an apparatus (or a system) using the unlicensed band frequency should perform a clear channel assessment (CCA) and decide whether or not a channel is used depending on a CCA result. In this case, a channel occupancy time may be limited depending on a frequency regulation even though the channel is occupied depending on the CCA result, the channel may not be occupied for a time exceeding a maximum channel occupancy time, and the CCA should be additionally performed in order to reoccupy the channel.
Due to the limitations of the unlicensed band system as described above, a scenario of installing/operating the licensed band system and the unlicensed band system in a form in which they are complementary to each other rather than a standalone system using only the unlicensed band in providing a mobile communication service has been reviewed. In this scenario, a control function requiring reliability, such as a terminal control, mobility management, and the like, is performed through the licensed band frequency, and a traffic function such as a wireless transmission speed increase, wireless traffic load balancing, and the like, is operated in a form in which the licensed band system is complemented using the unlicensed band system. For example, the control function and the traffic function are performed through a carrier of the licensed band, and the traffic function is performed through a carrier of the unlicensed band.
The operations of the licensed band carrier and the unlicensed band carrier as described above may be implemented through a carrier aggregation (CA) technology of 3rd generation partnership project long term evolution (3GPP LTE). For example, there is a carrier aggregation scheme between an unlicensed band frequency division duplex (FDD) carrier and the licensed band carrier or a carrier aggregation scheme between an unlicensed band time division duplex (TDD) carrier in which both of an uplink and a downlink are operated and the licensed band carrier.
A cellular system using the unlicensed band may provide a mobile communication service of which a quality of service (QoS) is ensured using cheap and rich frequency resources and a high level interference control technology. However, in order to solve various regulations present in the unlicensed band and a problem of coexistence with another unlicensed band system and secure the advantages as described above, a new coexistence technology and interference control technology are required. Particularly, due to characteristics of the unlicensed band, an apparatus operated in the unlicensed band may occupy and use a channel. In this case, in the case in which the carrier aggregation is used in order to solve the coexistence with another device in the unlicensed band and a problem due to a restriction of an operation in the unlicensed band, characteristics of the licensed band and the unlicensed band should be simultaneously considered. In addition, a service having reliability similar to that of an existing cellular service should be provided by reflecting limitations (characteristics) for operating an apparatus in the unlicensed band.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.